Ignition system in pneumatic acoustic source



March 24, 1970 J. M. PURSELL IGNITION SYSTEM IN PNEUMATIC ACOUSTIC SOURCE 5 Sheets-Sheet 1 Filed Feb. 27. 1969 L L R "a m m N 2 N U R E JwO WM w 4 G A 2 I L F E S R M PRESSURE CHAMBER AIR SUPPLY March 24, 1970 J. M. PURSELL 3,502,170

IGNITION SYSTEM IN PNEUMATIC ACOUSTIC SOURCE Filed Feb. 27. 1969 5 Sheets-Sheet 2 FIG. 5

INVENTOR JARSEL M. PURSELL March 24, 1970 J. M. PURSELL 3,502,170

IGNITION SYSTEM IN PNEUMATIC ACOUSTIC SOURCE Filed Feb. 27, 1969 5 Sheets- Sheet 3 37b eve J L an I I FIG. 7

INVENTOR JARSE L M. PURSELL ATTOR NEY March 24, 1970 M. PURSELL 3,502,170

IGNITION SYSTEM IN PNEUMATIC ACOUSTIC SOURCE Filed Feb. 27, 1969 5 Sheets-Sheet 4 I k 1; x

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3,502,170 IGNITION SYSTEM IN PNEUMATIC ACOUSTIC SOURCE Jarsel M. Pursell, Dallas, Tex., assignor to Mobil Oil Corporation, a corporation of New York Filed Feb. 27, 1969, Ser. No. 802,945 Int. Cl. G01v 1/06 US. Cl. 181-5 9 Claims ABSTRACT OF THE DISCLOSURE The specification discloses a repetitive acoustic source having a chamber in which an air-diesel fuel mixture is ignited to form high pressure gases which are rapidly released through a port by a quick-acting valve to generate an acoustic pulse in water. The fuel mixing and ignition system comprises an arrangement for injecting air into the chamber, a plurality of diesel fuel injectors, and a plurality of electrically energized igniters. Located adjacent each igniter is a block of carbon which, after the initial operation of the source, becomes heated to a temperature sufiicient to ignite the air-diesel fuel mixture. The electrical igniters then are de-energized and the carbon blocks are employed to perform the function of igniting the air-diesel fuel mixture introduced in the chamber in subsequent cycles of operation.

BACKGROUND OF THE INVENTION This invention relates to an ignition system in a pneumatic acoustic source for generating acoustic pulses repetitively in water for marine seismic operations.

In US. Patent No. 3,397,755, Pneumatic Seismic Source, issued Aug. 20, 1968, and US. patent application Ser. No. 663,663, Fuel Mixing and Ignition System in Pneumatic Acoustic Source, filed Aug. 28, 1967, now Patent No. 3,434,561, by George B. Loper and assigned to the same assignee as that of the present invention, there is disclosed a repetitive pneumatic acoustic source for marine seismic operations and which comprises a rigid chamber having an outlet port which is opened and closed by a fast-acting valve. In operation, the valve is moved to close the port, and the chamber is pressurized with high gas pressure. The valve then is actuated to open the port to allow the pressurized gas to be released rapidly into the water to generate an acoustic pulse. This cycle is repeated periodically to generate repetitive acoustic pulses in water.

In one embodiment, air and fuel injection means and igniters are provided for pressurizing the chamber. Air and fuel are injected into the chamber to form a combustible mixture which is ignited to form hot gases of increased pressure. The igniters are electric igniters continuously energized by a source of current located on the towboat.

SUMMARY OF THE INVENTION In accordance with the present invention, in a pneumatic acoustic source of the type having fuel injection means and initiating igniting means, carbon means is provided for performing the ignition function after the initial period of operation of the source. The carbon means is positioned to be exposed to the temperature formed in the chamber States atent 3,502,170 Patented Mar. 24, 1970 BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 illustrates a pneumatic acoustic source in the environment in which it is to be used;

FIGURE 2 is a cross-sectional view of the acoustic source showing a side view of the quick-acting valve in the pressure chamber, a fuel injection and ignition system in the chamber, and a schematic illustration of the equipment employed for operating the source;

FIGURE 3 is an enlarged end view of a carbon liner of the present invention;

FIGURE 4 illustrates the ignition system of the present invention employing the carbon liner of FIGURE 3;

FIGURE 5 is an end view of FIGURE 4 taken along the lines 55 thereof;

FIGURE 6 is an enlarged view of a plate employed for holding the carbon liner to a shield forming the ignition system;

FIGURE 7 is an end view of FIGURE 6 taken along the lines 77 thereof;

FIGURE 8 is a cross-sectional view of the acoustic source and its quick-acting valve;

FIGURE 9 is a cross-sectional view of FIGURE 2 taken along the lines 99 with the quick-acting valve removed; and

FIGURE 10 is a schematic diagram of the acoustic source and instrumentation used to control the source.

OPERATION AND DESCRIPTION OF ACOUSTIC SOURCE Referring now to FIGURE 1, the acoustic source 20 to which the present invention is directed is shown supported in water from a boat 21 by a cable arrangement 22 and supporting arms 23. As can be seen from the cross-sectional view of FIGURE 2, the acoustic source comprises enclosing wall structure 24 forming a pressure chamber 25 and which has a port at the lower end to be coupled to water. The outlet port comprises aperture 26 formed at the lower end of enclosing wall structure 24 and a plurality of laterally extending slots 27 extending through cylinder 28. A quick-opening, spool-shaped valve 30 is provided for opening and closing the outlet port. When the valve is in a closed position, the chamber is pressurized with high gas pressure. At a desired time, the valve 30 is actuated for sudden downward movement to allow the high pressure gas to escape rapidly into the water by way of the outlet port to generate an acoustic pulse. Retract means is provided to move the valve 30 to its closed position following the generation of an acoustic pulse whereby the cycle is repeated for the generation of subsequent acoustic pulses. In one embodiment, each cycle is of the order of six seconds whereby acoustic pulses are generated in water at a repetition rate of ten per minute.

The arrangement for pressurizing the chamber comprises a main air inlet 31 for injecting air into the chamber in a swirling, clockwise path, a plurality of fuel injectors 32 for injecting diesel fuel into the chamber for mixture with the air, and a plurality of ignition means 33 for igniting the resulting air-diesel fuel mixture formed. Each fuel injector 32 is positioned to spray fuel toward an associated ignition means. Each ignition means 33 has a shield 34 located on one side thereof between the ignition means and the air flowing toward the igniter in the clockwise direction. These shields are provided to shield or protect the ignition means from the cooler air injected into the chamber.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGURES 35, each ignition means 33 comprises an electric igniter 35 and a carbon member 36, the latter of which is coupled to each shield and located adjacent each igniter. These carbon members are employed to prolong the lifetime of the igniters. They are half-cylinders in shape and coupled to the interior surface of the half-cylindrical-shaped shields 34 whereby they do not obstruct the path of diesel fuel flow toward the igniters 35. In the initial period of operation of the source, the carbon members 36 are heated by the igniters and by the hot gases formed within the chamber whereby the carbon members begin to glow. At this time, they reach a temperature which is sufficient to ignite the airdiesel fuel mixture introduced into the chamber. When this occurs, the power supply to the igniters 35 is cut off. Since the time of each cycle of operation of the source is only six seconds, the carbon members 36 retain enough heat, until the subsequent cycle, following cutoff of the igniters 35, to ignite and burn the next charge of airdiesel fuel mixture introduced into the chamber. As the charge burns, the carbon members are again reheated to a higher temperature by the hot gases, and a regenerative action takes place whereby the carbon members are able to ignite and burn subsequent charges of air-diesel fuel mixtures introduced into the chamber of the source.

Thus, following the initial operation of the acoustic source, the carbon members relieve the electrical igniters 35 of the ignition function. The carbon members thereby prolong the lifetime of the igniters 35, which if energized continuously would have a much shorter lifetime than the carbon members. Thus, a substantial amount of breakdown and repair time is saved as well as cost of replacing the igniters 35.

When it is desired to shut the acoustic source down, the main air supply and the supply of diesel fuel are shut off. In one embodiment, the power to the igniters 35 may be cut off after about ten minutes of initial operation of the source. This time is suflicient to allow the carbon members to heat up to the temperature necessary to ignite the air-diesel fuel charges introduced into the chamber. The carbon members 36 employed were formed from graphite commercially available from POCO Graphite Inc., 1200 Jupiter Road, Garland, Tex., and were impregnated with titanium carbide.

The carbon members employed had a length of about 1 /2 inches, an internal radius of 91 inch, and an external radius of 3 inch. The pointed ridges indicated at 36' were formed to increase the rate of heating of the carbon and to provide points of high temperature to enhance ignition of the air-diesel fuel mixture.

As can be seen in FIGURES 4 and 5, two metal plates 37 are secured to the fiat edges of the cylindrical shield 34 for holding the carbon member against the shields inner circular surface. These plates are shown in more detail in FIGURES 6 and 7. They are secured to the shield 34 by way of metal bolts 38 which extend through apertures 39 of plates 37. Extending edge 37a of each plate abuts against the outer circular surface of the shield 34, while the opposite edge 37b abuts against the inner circu lar surface of the carbon member 36, thereby holding it against the inner surface of the shield 34. Edge members 37c and 37d also serve to hold the carbon member 36 in place and prevent it from sliding along the inner surface of the shield 34.

Referring now to FIGURES 2 and 8, there will be described in more detail the source 20 and its method of operation. The valve 30 comprises a lower release piston or rim 41, interconnecting tubular member 42, and an upper or valve control rim 43. Tubular member 42 has an upper extension 44 and an aperture 45 extending axially therethrough. The valve 30 is supported for axial movement from a closed position, as shown in FIGURES 2 and 8, to a downward open position whereby lower rim 41 is positioned near the lower end of cylinder 28. When the valve 30 is moved to a closed position, the outlet port is sealed by lower piston ring seals 46 coupled to lower rim 41. In this position, the chamber 25 is pressurized by the arrangement described above and comprising air injected through inlet 31, fuel injectors 32, and ignition means including electric igniters 35 and carbon liners 36. Compressed air is applied to inlet 31 from air supply 56, solenoid-controlled valve 51, conduit 52, and check valve 53.

In the valves closed position, a control annulus is formed between the top surface of control rim 43 and the upper chamber structure 61 of the source. Upper seal 62, coupled to the chamber structure 61, contacts the upper surface of control rim 43 to seal the annulus from high gas pressure in the main chamber 25. Annulus 60 normally is maintained at a low pressure when the valve 30 is closed by an arrangement including normally closed solenoid valves 64 and shuttle valves 65, which vent annulus 60 to the water by way of passageways 66, valves 65, and vents 67. The area of the control rim 43 within the upper seal 62 is greater than the area of release rim 41 within the lower seal 46. Thus, a net upward force is applied to the quick-opening valve maintaining it in a closed position as the chamber 25 is pressurized.

The fast-acting valve 30 is actuated to release the pressurized gas from the chamber by increasing the pressure in control annulus 60. This is done by simultaneously opening solenoid valves 64, of a dual triggering system, to allow air to flow from conduit 52 to valves 65 by way of conduits 68, valves 64, check valves 69, and passageways 70. The air causes shuttle valves 65 to close vents 67 for fiow to annulus 60 through passageways 66. The increase in pressure in annulus 60 causes valve 30 to move downward to a position where the top surface of the control rim 43 disengages the upper seal 62. When this occurs, the high gas pressure in the chamber 25 acts upon the top surface of the control rim 43 to upset the balance of force and rapidly move the quickopening valve 30 downwardly to allow the high pressure gas in the chamber 25 to be released immediately to the water by way of aperture 26 and slots 27 to generate an acoustic pulse.

The fuel mixing and ignition system for pressurizing the main chamber 25 comprises four diesel fuel injectors 32 and four ignition means 33 alternately spaced and located in a first plane near the top of the source. Similarly, four diesel fuel injectors 32 and four ignition means 33 are located alternately in a second plane near the bottom of the source. The fuel injectors 32 and ignition means 33 are located at positions. whereby diesel fuel from each fuel injector 32 is sprayed toward an associated ignition means. In the embodiment disclosed, four upper fuel injectors 32 spray fuel toward four lower ignition means 33, respectively, and the lower fuel injectors 32 spray fuel toward the four upper ignition means, respectively. In FIGURES 2 and 9, the upward traveling fuel is indicated by the dotted lines while the downward traveling fuel is indicated by the dashed lines 81. Each associated fuel injector-ignition means pair is positioned whereby the direct line of sight between each pair is offset from the center of the Chamber whereby the tubular interconnecting member 42 does not interfere with the diesel fuel sprayed toward the igniters.

The main air inlet 31 is positioned to direct air into the pressure chamber upward toward the bottom surface of control rim 43 of the quick-acting valve to one side of the tubular interconnecting member 42. Upon striking the bottom surface of the control rim 43, the air is deflected around the chamber in a clockwise direction and downwardly in a swirling motion. The general direction of air flow is indicated in FIGURE 9 by curved arrow 82. The fuel injectors 32 and ignition means 33 are located whereby fuel is sprayed from an injector toward an associated igniter in a direction opposite the flow of clockwise air between the injector-igniter pairs in order to enhance mixing of the diesel fuel with the air.

Referring again to FIGURE 4, the shields 34 are metallic half cylinders welded to the interior chamber structure around apertures formed through the chamber structure and through which the igniters are inserted. The shields have inner and outer diameters of 1 /2 and 2 /2 inches, respectively, and a length of 2%, inches. Each igniter 35 is a General Electric glow plug, N0. 6A421G56, having an electrical coil 86 therein. These glow plugs have a diameter of about one-fourth inch and extend into the chamber 25 about two inches. The coil is coupled to a terminal 87 by way of electrical conductor or lead 88. The glow plug is supported in member 89 by support fit-- tings 90-92. Member 89 is threaded into fitting 93 welded to the exterior chamber structure for extension of the glow plug within the chamber 25 for ignition purposes. Electrical leads extending through connector 94 are clipped to terminal 87 for providing power for energizing the coil 86.

Referring now to FIGURE 10, a brief description will be given in the manner that the source and associated equipment operate to produce periodic pulses of acoustic energy in water. In this figure, the system to the left of dashed line is towed in the water during seismic operations while the equipment to the right of dashed line 100 is located and supported on the towboat. The air supply 50 comprises a diesel engine 101, a compressor 102, and a receiver 103. The output of this receiver is coupled to the source by way of conduit 104, solenoidcontrolled valve 51, and conduit 52. Air for retracting the quick-acting valve is continuously applied to a retract chamber (to be described later) by way of conduit 105, check valve 106, and a flexible conduit 107. The arrangement for applying diesel fuel to the source comprises an air-operated pump coupled to a fuel supply 111 by way of filter 112 and check valve 113. Pump 110 applies fuel to manifold 114 (see also FIGURE 8) by way of conduit 115 and check valve 116. Diesel fuel passes from manifold 114 to the fuel injectors 32 by way of check valves 117.

An arrangement also is provided for applying lubricating oil to the lower piston of the quick-acting valve. This arrangement comprises a second air-operated pump 120, coupled to an oil supply 121 by way of filter 122 and check valve 123. Pump applies lubricating oil to a lubricating oil manifold 124 (see also FIGURE 8) and conduits 125 by way of conduit 126 and check valve 127.

An electrically operated control system 130- sequentially controls solenoid-controlled valves 51 and 64 and in addition air-operated pumps 110 and 120 during each cycle of operation for the production of an acoustic pulse. For example, assuming that the quick-acting valve 30 is in a closed position, control system 130 applies a signal to valve 51 to open this valve for a short period of time to allow high pressure air from receiver 103 to be applied to the pressure chamber 25. During the air filling operation, control system 130 also operates air-operated pump 120 to pump lubricating oil into the chamber for a short period of time. Pump 120 then is inactivated and valve 51 cut off after the chamber 25 has been filled with air. Next,

control system 130 actuates pump 110 to inject diesel fuel into the pressure chamber for a short period of time. In the initial period of operation, igniters 35, coupled together in parallel, are energized by power applied thereto from transformer 131 and AC source 132. Thus, as soon as diesel fuel is injected into the chamber to form the combustible mixture, during each cycle, ignition starts and continues until a predetermined time (when the pressure no longer rises). Control system 130 then actuates solenoid-controlled valve 64 for a short period of time to allow air in conduit 52 to be applied to control annulus 60 to actuate the quick-acting valve 30 for releasing the high pressure gas from the pressure chamber 25 into the water to generate an acoustic pulse. After the high pressure gas is released into the water, the air applied to the retract chamber retracts the valve to its closed position and the cycle is repeated.

After about ten minutes of initial operation, the igniters 35 are de-energized by opening switch 133 whereby carbon liners 36 are allowed to take over in igniting the subsequent charges of air-diesel fuel mixtures introduces into the chamber 25.

When it is desired to shut the acoustic source down, the power to solenoid-controlled valve 51 and to the solenoid (not shown) which controls the air-operated pump 110 is shut off. When this occurs, the main air supply and the supply of diesel fuel are shut off, thereby stopping the operation of the acoustic source.

Referring again to FIGURE 8, there will be described details of the quick-acting valve structure, the valve retract mechanism, and valve deceleration system. These features also are disclosed and claimed in copending application by Bernard Otto, Repetitive Pneumatic Acoustic Source for Marine Seismic Surveying, Ser. No. 663,676, filed on Aug. 28, 1967, and assigned to the same assignee as the present invention. The arrangement for supporting the quick-acting valve centrally of the enclosing wall structure 24 and for movement axially thereof comprises a lower wear ring coupled to the lower rim 41 and an upper bearing member 141 coupled to the upper chamber structure. Wear ring 140 slides on the inner surface of slotted cylinder 28 which is made up of an inner slotted liner 28a and an outer slotted cylinder 28b. Bearing 141 supports and guides the upper extension 44 of the quickacting valve 30.

Extending centrally of the quick-acting valve 30 and supported rigidly with respect to the chamber wall structure 24 is a central member. This member comprises central support 142, tubular member 143, and slotted end cap 144 coupled together, respectively, and to the chamber wall structure by way of lower hub 145 and slotted cylinder 28. Central support member 142 has two keys 146 secured thereto by bolts 147 which cooperate with the slots 143 formed in the interior surface of the valve 30 for guiding the valve in its upward and downward movement. The exterior diameters of tubular member 143 and slotted end cap 144 are smaller than the interior diameter of the aperture 45 extending through the quick-acting valve 30, thereby providing a central region exposed to and containing water. Water may pass into and out of this region by way of the aperture 45 extending through the upper extension 44 of the valve 30 and by way of water slots 150 formed on the outer periphery of central support member 142. These water slots extend from the top portion of member 142 to apertures 151, the latter of which allow water to pass interiorly of member 142 intermediate its end. Thus, the central water region extends completely through the quick-acting valve 30 when it is in a closed position and cools the interconnecting member 42 from the hot temperatures generated within the pressure chamber 25.

Also located within the aperture 45 extending through the quick-acting valve 30 is a retract mechanism comprising an air chamber 152 formed by the tubular member 143 and in addition interior retract piston 153, the

latter of which is rigidly coupled to the quick-acting valve 30. This coupling is by way of stem 154, rim 155, a plurality of spaced spokes 156, and rim 157. Thus, the retract piston 153 moves with the quick-acting valve 30 and is supported for sliding movement within the rigidly supported member 143. The lower end of tubular memher 143 is closed by end portion 158, Pressurized air is injected into the retract chamber 152 by way of flexible conduit 107 (mentioned previously) and aperture 159 extending through stern 154. Thus, following the generation of an acoustic pulse and after the high pressure gas is released from the pressure chamber 25, the pressurized air in the retract chamber acts over the entire surface 160 of retract piston 153 and moves the piston 153 and hence the quickacting valve 30 to the closed position.

The arrangement for decelerating the valve comprises a lower water trapped region or chamber 161 for decelerating the quick-acting valve 30 at the end of its opening movement and an upper or return water trap chamber 162 for decelerating the quick-acting valve 30 at the end of its return movement.

Lower water trap region 161 is formed as the lower rim portion 163 slides around the enlarged cylindrical portion 164 of central support 142. Water trapped in this region decelerates the valve 30. Water escapes downward through the small clearance between the exterior surface of member 164 and the interior surface of member 163. The exterior surface of member 164 is tapered toward its upper end to provide a variable orifice to obtain uniform deceleration of the valve. Upon movement of the valve 30 downward, water below the lower rim 41 passes outward and downward by way of slots 27 and apertures 166 formed in connecting hub 145.

As the quick-acting valve and hence the retract piston 153 moves downward, water from the annular water region within the quick-acting valve 30 flows through laterally extending apertures 167, formed in end cap 144, into the chamber region 162. Upon upward movement of the valve 30 and the retract piston 153, Water trapped within this chamber decelerates the valve at the end of its return movement. It escapes through apertures 167 by way of the small clearance between the exterior surface of retract piston 153 and the interior surface of end cap 144. The exterior surface of retract piston 153 is tapered toward its upper end to provide a variable orifice to obtain uniform deceleration of the valve.

The upper seal 62 employed in the source is disclosed and claimed in copending United States application by Ellis M. Brown et al., Seal for Pneumatic Acoustic Source, Ser. No. 663,664, filed on Aug. 28, 1967, and assigned to the same assignee as that of the present invention. The seal comprises a resilient elastomer O-ring and a stainless steel ring, both of which are located and held within an annular slot formed in structure 61 and surrounding the annulus 60. The ealstomer O-ring is located between the walls of the slot and the steel ring, the latter of which has a lower end portion positioned to extend out of the slot downward to contact the top surface of control rim 43. This arrangement protects the elastomer O-ring from the high temperatures generated within the pressure chamber 25. Pressurized gas from the pressure chamber also is applied to one side of the elastomer O-ring for pressure sealing purposes. This pressure is applied to the O-ring by way of a labyrinth utilized to cool the high pressure gas before application to the elastomer O-ring. The labyrinth is formed in structure 61 and has passageways extending from chamber to the annular slot which holds the elastomer O-ring and steel ring,

The shuttle valves 65 mentioned above are disclosed and claimed in the aforementioned patent application by Bernard Otto. Each valve comprises a tubular member having two open ends and a closed wall formed intermediate the ends blocking the passageway through the tubular member. The valve is supported for reciprocal movement in a conduit whose two ends are connected to passageway 70 (FIGURE 2) and vent 67, respectively. Passageway 66 is connected to the conduit intermediate its ends. Apertures extend laterally through the side structure of the tubular member on each side of the wall but spaced therefrom. Normally, a spring biases the tubular member to a position whereby the apertures on the side of the wall facing vent 67 are positioned over the passageway 66, thereby connecting passageway 66 and hence annulus to vent 67. In this position, the wall also blocks passageway from passageway 66. When valves 64 are actuated, air flows through passageway 70 and acts on the other side of the wall to move the shuttle valve toward the vent 67 to position the apertures on this latter side of the wall over passageway 66 to allow air to flow to annulus 60 for triggering purposes. In this latter position, the wall in the shuttle valve blocks vent 67 from passageway 66.

\Vhat is claimed is: 1. An acoustic source for repetitively generating high energy acoustic pulses in water for exploratory purposes comprising:

wall structure forming a pressure chamber to be immersed in water and having an outlet port for releasing high pressure gas from said chamber,

movable valve means for opening and closing said outlet port,

means for introducing combustible fluid into said chamber,

initiating igniting means for igniting said combustible fluid to form hot gases of high pressure in said chamber, means for actuating said valve means to move said valve means rapidly to an open position to open said outlet port to allow said high gas pressure formed in said chamber to be released rapidly from said chamber to generate an acoustic pulse in water,

means for moving said valve means to a closed position following the generation of an acoustic pulse to allow repetitive acoustic pulses to be generated in water in subsequent cycles of operation, and

carbon means exposed to the temperature formed in said chamber for providing ignition heat after an initial period of operation of said source for igniting the combustible fluid introduced into said chamber in subsequent cycles of operation whereby said initiating igniting means may be relieved of its ignition function.

2. An acoustic source for repetitively generating high energy acoustic pulses in water for exploratory purposes comprising:

wall structure forming a pressure chamber to be immersed in water and having an outlet port for releasing high pressure gas from said chamber,

movable valve means for opening and closing said outlet port,

means for introducing combustible fluid into said chamber,

initiating igniting means,

energizing means for energizing said initiating igniting means to provide ignition heat for igniting said combustible fluid to form hot gases of high pressure in said chamber,

means for actuating said valve means to move said valve means rapidly to an open position to open said outlet port to allow said high gas pressure formed in said chamber to be released rapidly from said chamber to generate an acoustic pulse in water,

means for moving said valve means to a closed position following the generation of an acoustic pulse to allow repetitive acoustic pulses to be generated in water in subsequent cycles of operation, and

carbon means exposed to the temperature formed in said chamber for providing ignition heat after an initial period of operation of said source for igniting the combustible fluid introduced into said chamber in subsequent cycles of operation whereby said initiating igniting means may be de-energized following said initial period.

3. The system of claim 2 wherein:

said carbon means is located adjacent said ignition means.

4. The system of claim 2 comprising:

a plurality of carbon means located in said chamber and exposed to the hot gases formed in said chamber for providing ignition heat after an initial period of Operation of said source for igniting the combustible fluid introduced into said chamber in subsequent cycles of operation whereby said initiating igniting means may be de-energized following Said initial period.

5. The system of claim 2 comprising:

a plurality of initiating igniting means located in said chamber,

said energizing means being coupled to said plurality of initiating igniting means for energizing said plurality of initiating igniting means, and

carbon means located in said chamber adjacent each initiating igniting means and exposed to the temperature formed in said chamber for providing ignition heat after an initial period of operation of said source for igniting the combustible fluid introduced into said chamber in subsequent cycles of operation whereby said initiating igniting means may be de-energized following said initial period.

.6. In an acoustic source for generating high energy acoustic pulses in water for exploratory purposes comprising:

wall structure forming a pressure chamber to be immersed in water and having an outlet port for releasing high pressure gas from said chamber,

movable valve means for opening and closing said out let port,

means for injecting air in a flow path in said chamber,

ignition means located in said flow path,

said ignition means including an electric igniter,

means for energizing said electric igniter for providing ignition heat in said chamber,

said air flowing toward said ignition means predominantly from a predetermined direction,

shield means positioned in said flow path adjacent said ignition means to shield said ignition means from air flowing from said predetermined direction to reduce cooling of said ignition means,

said shield means being located adjacent said ignition means on the side facing said direction from which said air is flowing in said flow path toward said ignition means,

fuel injection means for injecting combustible fuel into said chamber for mixture with said air to form a combustible mixture for ignition to form a high gas pressure in said chamber,

said fuel injection means being positioned to inject combustible fuel toward said ignition means at a side thereof unobstructed by said shield means,

means for actuating said valve means to move said valve means rapidly to an open position to open said outlet port to allow said high gas pressure formed in said chamber to be released rapidly from said chamber to generate an acoustic pulse in water, and

means for moving said valve means to a closed position following the generation of an acoustic pulse to allow repetitive acoustic pulses to be generated in water in subsequent cycles of operation,

the combination therewith of:

carbon means located between said electric igniter and said shield and exposed to the temperature formed in said chamber for providing ignition heat after an initial period of operation of said source for igniting the combustible mixture formed in said chamber in subsequent cycles of operation following said initial period whereby said electric igniter may be de-energized following said initial period.

7. The combination of claim 6 wherein:

said carbon means is coupled to and supported by said shield means.

8. The combination of claim 6 comprising:

a plurality of spaced ignition means located in said chamber,

each ignition means including an electric igniter,

said energizing means being coupled to each of said igniters for energizing said igniters for providing ignition heat in said chamber,

a shield located adjacent each ignition means on a side facing the direction from which air is flowing toward an associated ignition means,

a plurality of spaced fuel injectors for injecting combustible fuel into said chamber for mixture with said air to form a combustible mixture for ignition to form a high gas pressure in said chamber,

one of each of said fuel injectors being positioned to inject combustible fuel toward one of said ignition means at a side thereof unobstructed by its associated shield, and

carbon means located between each igniter and its associated shield and exposed to the temperature formed in said chamber for providing ignition heat after an initial period of operation for igniting the combustible mixture formed in said chamber in subsequent cycles of operation whereby said electric igniters may be de-energized following said initial period,

each carbon means coupled to and supported by one of said shields.

9. In an acoustic source for generating high energy acoustic pulses in water for exploratory purposes having:

wall structure forming a pressure chamber to be immersed in water and having an outlet port for releasing high pressure gas from said chamber.

movable valve means for opening and closing said outlet port,

means for injecting air in a flow path in said chamber,

ignition means located in said flow path,

said ignition means including an electric igniter,

means for energizing said electric igniter for providing ignition heat in said chamber,

said air flowing toward said ignition means predominantly from a predetermined direction,

shield means positioned in said flow path adjacent said ignition means to shield said ignition means from air flowing from said predetermined direction to reduce cooling of said ignition means,

said shield means being located adjacent said ignition means on the side facing said direction from which said air is flowing in said flow path toward said ignition means,

fuel injection means for injecting combustible fuel into said chamber for mixture with said air to form a combustible mixture for ignition to form a high gas pressure in said chamber,

said fuel injection means being positioned to inject combustible fuel toward said ignition means at a side thereof unobstructed by said shield means,

means for actuating said valve means to move said valve means rapidly to an open position to open said outlet port to allow said high gas pressure formed in said chamber to be released rapidly from said chamber to generate an acoustic pulse in water,

means for moving said valve means to a closed position following the generation of an acoustic pulse to allow repetitive acoustic pulses to be generated in water in subsequent cycles of operation, and

ll 12 carbon means located between said electric igniter and after said initial period, de-energizing said igniter said shield and exposed to the temperature formed to allow said carbon means to ignite the comin said chamber for providing ignition heat after an bustible mixture introduced into said chamber initial period of operation of said source for ignitduring subsequent cycles of operation.

ing the combustible mixture formed in said chamber in subsequent cycles of operation following said References Cited "11ml Penod: UNITED STATES PATENTS the method of operating said source WhlCl'l comprises:

initially applying energizing current to said igniter 314341562 3/1969 Johnson for igniting the combustible mixture introduced 10 i into said chamber during said initial period of RICHARD FARLEY Pnmary Exammsr operation of said source, and C. E WANDS, Assistant Examiner 

